The present invention relates to a process for alkylation of an aromatic compound having at least one hydroxyl group on the aromatic ring, such as phenol, catechol, anisole, cresol, resorcinol or mixtures thereof, to provide an aromatic product having both hydroxyl and alkyl groups on the same aromatic ring in which the content of the para-alkyl isomer is high. The alkylated products are useful in making detergents for lubricating oils.
In accordance with the present invention, there is provided a process for producing alkylated, hydroxyl-containing aromatic compounds, said process comprising:
(a) isomerizing a normal alpha-olefin or mixture of normal alpha-olefins having from about 16 to about 30 carbon atoms in the presence of a first acidic catalyst capable of inducing both olefin isomerization and skeletal isomerization to produce a mixture of isomerized olefins;
(b) alkylating a hydroxyl-containing aromatic compound with said mixture of isomerized olefins in the presence of a second acidic catalyst comprising a sulfonic acid resin catalyst or an acidic clay.
Also provided in accordance with this invention is a process for producing an alkylated hydroxyl-containing aromatic compound, said process comprising:
(a) isomerizing a normal alpha-olefin or mixture of normal alpha-olefins having from about 16 to about 30 carbon atoms in the presence of a first acidic catalyst capable of inducing both olefin isomerization and skeletal isomerization to produce a mixture of straight-chain and branched-chain isomerized olefins;
(b) alkylating an hydroxyl-containing aromatic compound selected from the group consisting of phenol, catechol, anisole, cresol, resorcinol and mixtures thereof with said mixture of isomerized olefins in the presence of a second solid, acidic catalyst comprising a sulfonic acid resin catalyst or an acidic clay.
Among other factors, the present invention is based on the discovery that olefin and skeletal isomerization of the normal alpha-olefin prior to alkylation of the hydroxyl-containing aromatic compound results in an alkylated product containing a high content of compounds in which the alkyl and hydroxyl groups are in the para position relative to each other.
In its broadest aspect, the present invention involves a process for producing alkylated aromatic compounds that have at least one hydroxyl and at least one alkyl group on the same aromatic ring. That process comprises isomerizing a normal alpha-olefin or mixture of normal alpha-olefins (referred to herein collectively as xe2x80x9cNAOxe2x80x9d) having from about 16 to about 30 carbon atoms in the presence of a first solid, acidic catalyst capable of inducing both olefin isomerization and skeletal isomerization to produce a mixture of isomerized olefins, then alkylating an aromatic compound having at least one hydroxyl group on the aromatic ring with the mixture of isomerized olefins in the presence of a second solid, acidic catalyst comprising a sulfonic acid resin catalyst or an acidic clay.
The alkylation of phenol with olefins, under normal alkylation conditions using a macroporous sulfonic acid resin catalyst or acidic clay, nominally affords an alkylated phenol product in which the para and ortho isomers are dominant. When one uses a normal alpha-olefin to alkylate the phenol, the para isomer/ortho isomer ratio content is only about 50/50.
It has now been discovered that by isomerizing an NAO prior to using it to alkylate phenol (or other hydroxyl-containing aromatic compounds), a significant increase in the para isomer is obtained in the alkylated product, e.g., the para isomer/ortho isomer ratio can be increased to about 80/20. The alkylated product can be used to prepare detergents for lubricating oil, and the high para-isomer content allows more base to be added to the detergent.
The hydroxyl-containing aromatic compounds that are alkylated in the subject process include phenol, catechol, anisole, cresol, resorcinol and mixtures thereof, with phenol being the preferred compound.
The normal alpha-olefins that are isomerized prior to the alkylation of the hydroxyl-containing aromatic compounds are normal alpha-olefins or mixtures of normal alpha-olefins that have from about 16 to about 30 carbon atoms per molecule. Preferably, they have about 20 to about 28 carbon atoms per molecule.
The catalyst used to isomerize the normal alpha-olefin or mixture of normal alpha-olefins can be any catalyst that is capable of inducing both olefin isomerization and skeletal isomerization in the NAO while leaving the NAO otherwise essentially in tact. As used herein, the term xe2x80x9colefin isomerizationxe2x80x9d refers to movement of the carbon-carbon double bond within the molecule, and the term xe2x80x9cskeletal isomerizationxe2x80x9d refers to rearrangement of the carbon atoms within the molecule. Examples of such catalysts include solid, acidic catalysts comprising at least one metal oxide, and having an average pore size of less than 5.5 Angstroms. Preferably, the solid, acidic catalyst comprises a molecular sieve with a one-dimensional pore system. More preferably, it is selected from the group consisting of molecular sieves SM-3, MAPO-11, SAPO-11, SSZ-32, ZSM-23, MAPO-39, SAPO-39, ZSM-22, and SSZ-20. The preferred molecular sieves are SAPO-11 and SSZ-32. Other possible solid, acidic catalysts useful for isomerization include molecular sieves ZSM-35, SUZ4, NU-23, NU-87, and natural or synthetic ferrierites. These molecular sieves are well known in the art and are discussed in Rosemarie Szostak""s Handbook of Molecular Sieves (New York, Van Nostrand Reinhold, 1992), and U.S. Pat. No. 5,282,958, issued Feb. 1, 1994 to Santilli et al., both of which are hereby incorporated by reference.
The catalyst can be an admixture with at least one Group VIII metal. Preferably, the Group. VIII metal is selected from the group consisting of at least one of platinum and palladium, and optionally other catalytically active metals such as molybdenum, nickel, vanadium, tungsten, cobalt, zinc and mixtures thereof. More preferably, the Group VIII metal is selected from the group consisting of at least one of platinum and palladium. The amount of metal ranges from about 0.01% to about 10% by weight of the catalyst (not counting the weight of the metal), preferably from about 0.2% to about 5% by weight of the catalyst. The techniques of introducing catalytically active metals to the catalyst are disclosed in the literature, and pre-existing metal incorporation techniques and treatment of the catalyst to form an active catalyst such as ion exchange, impregnation or occlusion during preparation of the catalyst are suitable. Such techniques are disclosed in U.S. Pat. Nos. 3,236,761; 3,226,339; 3,236,762; 3,620,960; 3,373,109; 4,202,996; 4,440,996 and 4,710,485 which are incorporated herein by reference.
The xe2x80x9cmetalxe2x80x9d or xe2x80x9cactive metalxe2x80x9d as used herein means one or more metals in the elemental state or in some form such as sulfide, oxide or mixtures thereof. Regardless of the state in which the metallic component actually exists, the concentrations are computed as if they existed in the elemental state.
The catalyst is used in an amount effective to catalyze the isomerization reaction.
A preferred method of isomerizing the normal alpha-olefin or mixture of normal alpha-olefins involves catalytic isomerization using, for instance, a platinum-supported-on-SAPO-11 molecular sieve catalyst to partially isomerize a feed containing the NAO. This and related catalysts are described in U.S. Pat. No. 5,082,986, issued Jan. 21, 1992 to Miller, which is hereby incorporated by reference.
For platinum-on-SAPO-11 catalysts, partial isomerization is preferred. Therefore, preferred operating conditions include weight hourly space velocities (WHSV) between about 0.5 and about 10 at temperatures between about 100xc2x0 C. and about 250xc2x0 C. More preferred conditions include WHSV""s of between about 0.5 and about 5 at temperatures of about 120xc2x0 C. to about 160xc2x0 C.; most preferred conditions include WHSV""s of between about 0.5 and about 3.5 at temperatures of about 120xc2x0 C. to about 140xc2x0 C. Lower temperatures result in substantial olefin double bond migration, while higher temperatures result in increased skeletal rearrangement. The process is preferably conducted in the presence of added hydrogen.
The isomerized olefins contain branched-chain olefins. The branching may occur at a carbon atom that is part of the carbon-carbon double or at a carbon atom that does not form part of the double bond. Examples of the branched-chain olefins include, but are not limited to, the following: 
where R is the remainder of the olefin. Preferably, at least 70% of the isomerized olefins are branched, more preferably at least 90%. It has also been found that the more vinylidene and tri-substituted olefin isomers there are in the isomerized olefin mixture, the higher the para/ortho ratio will be in the alkylated product.
The second acidic catalyst is a solid catalyst comprising a sulfonic acid resin catalyst or an acidic clay. The sulfonic acid resin catalyst is an anionic ion exchange resin such as Amberlyst 15 and Amberlyst 36 sulfonic acid ion exchange resins sold by Rohm and Haas Co. Acidic clays such as Filtrol-24 can also be used. The catalyst is employed in an amount sufficient to catalyze the alkylation of the hydroxyl-containing aromatic compound. Typically, the amount of catalyst used will be about 1 wt. % to about 20 wt. %, based on the weight of the hydroxyl-containing aromatic compound.
The alkylation reaction is typically carried out with an hydroxyl-containing aromatic compound or mixture of hydroxyl-containing compounds and a mixture of isomerized olefins in hydroxyl-containing aromatic compound:isomerized olefin molar ratios from 1:15 to 25:1. Process temperatures can range from about 90xc2x0 C. to about 150xc2x0 C. Since the olefins have a high boiling point, the process is preferably carried out in the liquid phase. The alkylation process may be carried out in batch or continuous mode. In the batch mode, a typical method is to use a stirred autoclave or glass flask which may be heated to the desired reaction temperature. A continuous process is most efficiently carried out in a fixed bed process. Space rates in a fixed bed process can range from about 0.01 to about 10 or more WHSV.
In a fixed bed process the catalyst is charged to the reactor and activated or dried at a temperature of at least 100xc2x0 C. under vacuum or flowing inert, dry gas. After activation, the catalyst is cooled to ambient temperature and a flow of the hydroxyl-containing aromatic compound is introduced. Optionally, the hydroxyl-containing aromatic compound may be added to the catalyst at the reaction temperature. A flow of the isomerized olefin is then mixed with the hydroxyl-containing aromatic compound and allowed to flow over the catalyst. The reactor effluent containing alkylate product and excess hydroxyl-containing aromatic is collected. Excess hydroxyl-containing aromatic is then removed by distillation, stripping, evaporation under vacuum, or other means known to those skilled in the art .